In general, there are two kinds of error recovery schemes, namely an ARQ (Automatic Retransmission Request) method and an FEC (Forward Error Correction) method. In the ARQ method, a receiving end carries out error detection in accordance with a redundant code that has been added by a transmitting end, so that, in case an error is detected, a retransmission request for a packet, which relating to the error, is transmitted to the transmitting end. Consequently, in the ARQ method, the transmission end retransmits the packet relating to the error. The FEC method carries out error correction at the receiving end referring to the redundant code added by the transmitting end.
Moreover, for example, a hybrid ARQ method, in which the ARQ method and the FEC method are combined, is proposed in “A Two-Step Adaptive Error Recovery Scheme for Video Transmission over Wireless Networks”: Daji Qiao and Kang G. Shin, IEEE INFOCOM 2000. In the hybrid ARQ method, the transmission end adds a block error correction code (RS code), while the receiving end carries out error correction in accordance with the information of the RS code. The receiving end transmits a positive ACK signal or a negative ACK signal to the transmitting end, depending on the result of the error correction. The transmitting end retransmits a packet relating to the error when the transmitting end receives the negative ACK signal or when none of the positive and negative ACK signal is received in a time-out interval.
A high bit error rate makes it difficult to achieve an almost-error-free state without carrying out the retransmission, even if an error correction code having high correction ability is used. Therefore, it is necessary in general to have a joint code in which a convolutional code and a block code are combined, or a process such as inter-leave. This increases a size of a circuit and requires a large number of buffers in the transmitting and receiving ends.
Furthermore, in the above literature, the retransmission request is transmitted in case the error cannot be corrected by the error-correction process of the receiving end, and the retransmission is carried out per packet. However, in this method, the length of packet is significantly long (800 to 900 bits) and requires many bands for carrying out the retransmission once.